1. Field of the Invention
The invention relates to a device for measuring the mass rate of flow which works according to the Coriolis principle, with a measurement tube and a vibration generator and/or a vibration sensor for exciting and detecting vibrations of the measurement tube, the vibration generator and the vibration sensor having a magnet coil with a bobbin and a winding attached to it.
2. Description of Related Art
Devices for measuring the mass rate of flow using the Coriolis principle are well known from the prior art. In this connection, there are devices with only a single measurement tube or with several, often two parallel measurement tubes, and the measurement tube or measurement tubes can be made straight or looped. Devices for measuring the mass rate of flow using the Coriolis principle require that the measurement tube be sent into vibration and that the vibrations which result when flow takes place through the measurement tube be detected.
Magnet coils are often designed to excite vibrations of the measurement tube or to detect vibrations of the measurement tube. If such a magnet coil is exposed to a current, it generates a magnetic field; this field results in a force being exerted on the magnet located within the magnet coil. Based on this principle, the measurement tube of a device for measuring the mass rate of flow using the Coriolis principle can be excited to vibrations.
However, by applying a current to the magnet coil, therefore based on the fact that a current flows through the winding of the magnet coil provided on the bobbin, heating of the magnet coil occurs. It is necessary to limit this temperature rise especially for applications of a device for measuring the mass rate of flow using the Coriolis principle in explosion-prone areas.
The prior art generally discloses limiting the temperature rise of the magnet coil by dissipating the resulting heat onto a larger surface than the surface given by the magnetic field itself. Especially for high power applications, it is thus provided that the heat be dissipated from the magnet coil by its being routed to a generally metallic heat sink by means of a jacket or an enclosure with high thermal conductivity. Thus, the heat flow away from the magnet coil into the vicinity of the magnet coil is facilitated, by which the surface temperature of the magnet coil is reduced. However, this procedure is disadvantageous with respect to its relatively high costs and reduced efficiency as a result of formation of eddy currents in the metallic heat sink.